1. Field of the Invention
The present invention generally relates to collapsible and stackable bags and methods for stacking collapsible bags. More particularly, the invention relates to collapsible bags which are capable of being stacked when filled and methods of forming the bags to facilitate stacking.
2. Description of the Related Art
Bags capable of standing substantially upright are generally known in the art. For example, U.S. Pat. No. 4,934,255 to Boots, which is incorporated by reference herein, discloses flexible containers made of plastic film comprising a tubular outer envelope and an inner member affixed to the outer envelope. The inner member, which is at least 30% of the height of the outer envelope, provides outer spaces between the inner member and the outer envelope that are in open communication with an interior space within the inner member. As a result, material deposited in the containers described in the Boots patent fills the inner and outer spaces. This construction enables the inner and outer spaces to function like columns so that the bags stand substantially upright when filled.
Typically, when conventional bags of the Boots construction are filled and closed, air is captured in the top of the bag. The entrained air prevents the top of the conventional bag from collapsing onto the contents of the bag to provide a level surface for stacking.